Immunohistochemical investigation of a pulmonary surfactant in fatal mechanical asphyxia

We evaluated the usefulness of pulmonary surfactant protein A (SP-A) as a p ractical diagnostic marker of fatal mechanical asphyxia in forensic autopsy cases. A total of 27 cases of asphyxia were examined histologically and im munohistochemically and compared with a control group consisting of 16 case s of poisoning (n = 9) and peracute death (n = 7). Both groups showed histo logical findings of local atelectasis and local emphysema, congestion intra -alveolar and interstitial edema in most cases and pulmonary hemorrhages in some cases. The mechanical asphyxia group showed a significantly increased intensity of SP-A staining in the intra-alveolar space accompanied by many massive aggregates in approximately 60% of cases, which was not found in t he control group. These structures may be interpreted as aggregates of pulm onary surfactant released from the alveolar wall due to enhanced secretion caused by strong forced breathing or over-excitement of the autonomic nervo us system by mechanical asphyxia. The results of our investigation suggest the practical usefulness of the immunohistochemical detection of SP-A in di stinguishing mechanical asphyxia from other types of hypoxia.